Step-to-step wedge thread connections and related methods

ABSTRACT

A threaded connection includes a pin member comprising a first pin step and a second pin step, and pin wedge threads disposed on each of the first and second pin steps and a box member comprising a first box step and a second box step, and box wedge threads disposed on each of the first and second box steps, wherein an axial separation of the first and second pin steps differs from an axial separation of the first and second box steps.

BACKGROUND

1. Field of the Disclosure

Embodiments disclosed herein relate generally to threaded connections.More particularly, embodiments disclosed herein relate to two-step wedgethread connections and related methods of makeup.

2. Background Art

Casing joints, liners, drill pipe, and drill collars (collectivelyreferred to as “tubulars”) are often used in drilling, completing, andproducing a well. Casing joints, for example, may be emplaced in awellbore to stabilize a formation, to protect a formation againstelevated wellbore pressures (e.g., wellbore pressures that exceed aformation pressure), and the like. Casing joints may be coupled in anend-to-end manner by threaded connections, welded connections, and otherconnections known in the art. The connections may be designed so as toform a seal between an interior of the coupled casing joints and anannular space formed between exterior walls of the casing joints andwalls of the wellbore. The seal may be, for example, an elastomeric seal(e.g., an o-ring seal), a metal-to-metal seal formed proximate theconnection, or similar seals known in the art. In some connections,seals are formed between the internal and external threads. Connectionswith this characteristic are said to have a “thread seal.” As usedherein, a “thread seal” means that a seal is formed between at least aportion of the internal thread on the box member and the external threadon the pin member.

It will be understood that certain terms are used herein as they wouldbe conventionally understood where tubular joints are being connected ina vertical position along a central axis of the tubular members such aswhen making up a pipe string for lowering into a well bore. Thus, theterm “load flank” designates the side wall surface of a thread thatfaces away from the outer end of the respective pin or box member onwhich the thread is formed and supports the weight (i.e., tensile load)of the lower tubular member hanging in the well bore. The term “stabflank” designates the side wall surface of the thread that faces towardthe outer end of the respective pin or box member and supports forcescompressing the joints toward each other such as the weight of the uppertubular member during the initial makeup of the joint or such as a forceapplied to push a lower tubular member against the bottom of a bore hole(i.e., compressive force). The term “face” of the box is the end of thebox member facing outward from the box threads and the term “nose” ofthe pin is the end of the pin member facing outward from the threads ofthe connection. Upon makeup of a connection the nose of the pin isstabbed into and past the face of the box.

One type of thread commonly used to form a thread seal is a wedgethread. In FIGS. 1A and 1B, a connection 100 having a wedge thread isshown. “Wedge threads” are characterized by threads that increase inwidth (i.e., axial distance between load flanks 125 and 126 and stabflanks 132 and 131) in opposite directions on the pin member 101 and boxmember 102. Wedge threads are extensively disclosed in U.S. Pat. No. RE30,647 issued to Blose, U.S. Pat. No. RE 34,467 issued to Reeves, U.S.Pat. No. 4,703,954 issued to Ortloff, and U.S. Pat. No. 5,454,605 issuedto Mott, all assigned to the assignee of the present invention andincorporated herein by reference.

On the pin member 101, the pin thread crest 122 is narrow towards thedistal end of the pin member 101 while the box thread crest 191 is wide.Moving along the axis 105 (from right to left), the pin thread crest 122widens while the box thread crest 191 narrows. The rate at which thethreads change in width along the connection is defined by a variableknown as the “wedge ratio.” As used herein, “wedge ratio,” althoughtechnically not a ratio, refers to the difference between the stab flanklead and the load flank lead, which causes the width of the threads tovary along the connection. Furthermore, as used herein, a thread “lead”refers to the differential distance between a component of a thread onconsecutive threads. As such, the “stab lead” is the distance betweenstab flanks of consecutive thread pitches along the axial length of theconnection. In FIGS. 1A and 1B, the thread surfaces are tapered, meaningthat the pin thread 106 increases in diameter from beginning to endwhile the box thread 107 decreases in diameter in a complimentarymanner. Having a thread taper improves the ability to stab the pinmember 101 into the box member 102 and distributes stress in theconnection.

For wedge threads, a thread seal is accomplished by the contact pressurecaused by interference over at least a portion of the connection betweenthe pin load flank 126 and the box load flank 125 and between the pinstab flank 132 and the box stab flank 131, which occurs when theconnection is made-up. Close proximity or interference between the roots192 and 121 and crests 122 and 191 completes the thread seal when itoccurs over at least a portion of where the flank interference occurs.Higher pressure may be contained with increased interference between theroots and crests (“root/crest interference”) on the pin member 101 andthe box member 102 and by increasing flank interference. This particularconnection also includes a metal-to-metal seal that is accomplished bycontact between corresponding sealing surfaces 103 and 104 locating onthe pin member 101 and box member 102, respectively.

A property of wedge threads, which typically do not have a positive stoptorque shoulder on the connection, is that the make-up is“indeterminate,” and, as a result, the relative position of the pinmember and box member varies more for a given torque range to be appliedthan connections having a positive stop torque shoulder. As used herein,“make-up” refers to threading a pin member and a box member together. Afinal make-up refers to threading the pin member and the box membertogether up to a desired amount of torque, or based on a relativeposition (axial or circumferential) of the pin member with the boxmember.

For wedge threads that are designed to have both flank interference androot/crest interference at a selected make-up, both the flankinterference and root/crest interference increase as the connection ismade-up (i.e. increase in torque increases flank interference androot/crest interference). For wedge threads that are designed to haveroot/crest clearance, the clearance decreases as the connection ismade-up. Regardless of the design of the wedge thread, correspondingflanks and corresponding roots and crests come closer to each other(i.e. clearance decreases or interference decreases) during make-up.

Indeterminate make-up allows for the flank interference and root/crestinterference to be increased by increasing the torque on the connection.Thus, a wedge thread may be able to thread seal higher pressures of gasand/or liquid by designing the connection to have more flankinterference and/or root/crest interference or by increasing the torqueon the connection; however, this also increases stress on the connectionduring make-up, which could lead to failure during use.

Prior to make-up a flowing joint compound commonly referred to as “pipedope” is typically applied to surfaces of a threaded connection toimprove the thread seals and provide lubrication during make-up of theconnection. For example, the base (e.g., a grease) of the pipe dope mayassist a wedge-threaded connection in achieving a thread seal betweenload and stab flanks thereof, e.g., as disclosed in U.S. Pat. No. RE34,467 issued to Reeves. Further, pipe dope may contain metallicparticle additives, such as copper to protect the threads of the pin andbox members from friction galling during make-up and break-out.

When a wedge thread connection is made-up, excess pipe dope may becometrapped (rather than being squeezed out) between engaging pin and boxthreads, which may either cause false elevated torque readings (leadingto insufficient make-up or “stand-off”) or, in certain circumstances,damage the connection. Pipe stand-off due to inadequate evacuation ofthe pipe dope is detrimental to the structural integrity of wedge threadconnections. As the pressure build-up may bleed off during use, theconnection is at risk of accidentally backing off during use. Therefore,stand-off in wedge thread connections is of particular concern as it maylead to loss of seal integrity or even mechanical separation of the twoconnected members.

FIG. 2 shows a prior art two-step connection 150. The threads that formthe connection are separated on two different “steps,” a large stepindicated by the bracket 31 and a small step indicated by the bracket32. The portion between the large step 31 and the small step 32 iscommonly referred to as a mid-step 901. In some connections, themid-step 901 may be used as a metal-to-metal seal. The pin thread crest222 on the small step 32 of the pin member 101, at its full designheight, does not interfere with the box thread crest 221 on the largestep 31 of the box member 102 when the pin member 101 is stabbed intothe box member 102. The diameter of the small step 32 of the pin member101 is smaller than the smallest crest-to-crest thread diameter on thelarge step 31 of the box member 102. The pin thread 106 on the smallstep 32 can be stabbed past the box thread 107 on the large step 31. Thethreads on both the small step 32 and the large step 31, which havesubstantially the same nominal lead, engage with each revolution tomake-up the connection. Thus, the number of revolutions during which thethreads slide or rub against each other is reduced for the same numberof engaged threads. A two-step connection allows for each of the stepsto have threads with different characteristics as long there is littleor no variance in the nominal lead of the threads on the steps.

A two-step wedge thread connection is disclosed in U.S. Pat. No.6,206,436 issued to Mallis and assigned to the assignee of the presentinvention. That patent is incorporated herein by reference. Mallisdiscloses a two-step wedge thread connection having different wedgeratios, one of which is considered to be an “aggressive” wedge ratio andthe other a “conservative” wedge ratio. “Aggressive” refers to thelarger wedge ratio, and “conservative” refers to the smaller wedgeratio. Everything else the same, the greater the wedge ratio, the moredeterminate the make-up. Too large of a wedge ratio may have aninadequate wedging effect, which can allow the connection to back-offduring use. Smaller wedge ratios are better able to resist backing-offof the connection. Too small of a wedge ratio may have such anindeterminate make-up that galling may occur over the lengthened make-updistance. Mallis discloses that one of the steps can have a wedge ratiothat is optimized for a more determinate make-up (aggressive), while theother step can have a wedge ratio that is optimized for preventingback-off of the connection (conservative).

FIGS. 3A and 3B show cross-section views of a conventional two-stepwedge thread connection 200 prior to a final makeup. The connection 200includes a pin member 201 having pin wedge threads 106 thereon and a boxmember 202 having corresponding box wedge threads 107 thereon. Further,the connection 200 has first step 31 and second step 32, with a mid-stepregion 901 located therebetween. As shown, an axial separation of thetwo wedge thread steps 31, 32 of the pin member 201, indicated bydistance ‘B,’ is substantially equal to an axial separation of the twowedge thread steps 31, 32 of the box member 202, indicated by distance‘A.’ Thus, the pin wedge threads 106 on the first step 31 of the pinmember 201 may be characterized as “in-phase” with the box wedge threads107 on the first step 31 of the box member 202. Likewise, the pin wedgethreads 106 on the second step 32 of the pin member 201 may becharacterized as “in-phase” with the box wedge threads 107 on the secondstep 32 of the box member 202.

The corresponding pin and box threads on the two steps 31, 32 arein-phase such that during makeup, gaps 137 between approaching loadflanks 125, 126 are equal to gaps 138 between approaching stab flanks131, 132 on the first step 31. Similarly, gaps 137 between approachingload flanks 127, 128 are equal to gaps 138 between approaching stabflanks 133, 134 on the second step 32. Thus, corresponding load flanks125, 126 and stab flanks 131, 132 on first step and corresponding loadflanks 127, 128 and stab flanks 133, 134 on second step 32 will contactat substantially the same time (i.e., at final makeup). FIGS. 3C and 3Dillustrate the conventional two-step wedge thread connection 300 at afinal makeup. Because the corresponding load flanks 125, 126 and stabflanks 131, 132 on first step 31, and corresponding load flanks 127, 128and stab flanks 133, 134 contact at substantially the same time, theinterference generated between the surfaces is substantially equal.

A threaded connection having improved make-up and break-out torquecharacteristics would be appreciated by those skilled in the art.

SUMMARY OF THE DISCLOSURE

In one aspect, embodiments disclosed herein relate to a threadedconnection including a pin member comprising a first pin step and asecond pin step, and pin wedge threads disposed on each of the first andsecond pin steps and a box member comprising a first box step and asecond box step, and box wedge threads disposed on each of the first andsecond box steps, wherein an axial separation of the first and secondpin steps differs from an axial separation of the first and second boxsteps.

In other aspects, embodiments disclosed herein relate to a threadedconnection including a pin member comprising a first pin step and asecond pin step, and pin wedge threads disposed on each of the first andsecond pin steps and a box member comprising a first box step and asecond box step, and box wedge threads disposed on each of the first andsecond box steps, wherein the pin wedge threads on at least one of thefirst and second pin steps and the corresponding box wedge threads on atleast one of the first and second box steps are axially misaligned.

In other aspects, embodiments disclosed herein relate to a method ofmaking up a threaded connection, the method including rotationallyengaging a pin member having pin wedge threads with a box member havingcorresponding box wedge threads, wherein the pin and box wedge threadsare formed on corresponding first and second pin and box steps of thepin and box members and engaging opposing pin and box stab and loadflanks at different times during makeup of the threaded connection.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B show a cross-section view of a prior art connectionhaving a wedge thread.

FIG. 2 shows a cross-section view of a prior art two-step threadedconnection.

FIGS. 3A and 3B show cross-section and top views, respectively, of aprior art two-step wedge thread connection during makeup.

FIGS. 3C and 3D show cross-section and top views, respectively, of theprior art two-step wedge thread connection in FIGS. 3A and 3B at a finalmakeup.

FIGS. 4A and 4B show cross-section and top views, respectively, of areduced box step-to-step wedge thread connection during makeup inaccordance with one or more embodiments of the present disclosure.

FIGS. 4C and 4D show cross-section and top views, respectively, of thereduced box step-to-step wedge thread connection of FIGS. 4A and 4B at afinal makeup in accordance with one or more embodiments of the presentdisclosure.

FIGS. 5A and 5B show cross-section and top views, respectively, of areduced pin step-to-step wedge thread connection during makeup inaccordance with one or more embodiments of the present disclosure.

FIGS. 5C and 5D show cross-section and top views, respectively, of thereduced pin step-to-step wedge thread connection of FIGS. 5A and 5B at afinal makeup in accordance with one or more embodiments of the presentdisclosure.

FIG. 6 shows a cross-section view of a two-step wedge thread connectionhaving a vanishing box thread in accordance with one or more embodimentsof the present disclosure.

DETAILED DESCRIPTION

In one aspect, embodiments disclosed herein relate to threads fortubular connections. More particularly, embodiments disclosed hereinrelate to two-step connections having a step-to-step wedge by whichincreased interference is generated between opposing thread flanks at afinal makeup of the connection.

FIG. 4A shows a cross section of a two-step wedge thread connection 300having a step-to-step wedge in accordance with one or more embodimentsof the present disclosure. The connection 300 includes a pin member 301having pin wedge threads 306 and a box member 302 having correspondingbox wedge threads 307. The pin and box wedge threads 306, 307 may beconfigured having a dove-tailed profile. Further, the pin and boxmembers 301, 302 each have corresponding first steps 31 and second steps32 formed thereon and a mid-step region 901 located betweencorresponding steps 31, 32.

The connection 300 is configured such that an axial separation of thetwo wedge thread steps 31, 32 of the pin member 301, indicated bydistance ‘B,’ differs from an axial separation of the two wedge threadsteps 31, 32 of the box member 302, indicated by distance ‘A.’ Statedotherwise, an axial length of a mid-step region 901 located betweensteps 31, 32 of the pin member 301 may differ from an axial length of amid-step region 901 located between steps 31, 32 of the box member 302.As such, the pin wedge threads 306 on the first step 31 of the pinmember 301 may be characterized as “out-of-phase” with the correspondingbox wedge threads 307 on the first step 31 of the box member 302.Likewise, the pin wedge threads 306 on the second step 31 of the pinmember 301 may be characterized as “out-of-phase” with the correspondingbox wedge threads 307 on the second step 32 of the box member 302.

As used herein, a connection having axial length differences betweensteps may be referred to as the step-to-step wedge. Distances A and Bmay be measured from any fixed coaxial locations on pin and box membersfrom a first step 31 to a second step 32. As shown here, the coaxiallocations on the pin and box members are corresponding pin and boxthread flanks but those skilled in the art will understand otherlocations from which the distances may be measured.

In certain embodiments, distance A (i.e., axial separation of the twowedge thread steps 31, 32 of the box member 302) may be slightly lessthan distance B (i.e., axial separation of the two wedge thread segments31, 32 of the pin member 301). In this instance, the two-step wedgethread connection 300 may be termed a “reduced box step-to-step wedgethread connection” because the axial separation, distance A, betweensteps 31, 32 of the box member 302 is reduced. As shown, distance A ofthe box member 302 is reduced by a specified amount (i.e., x.xxxinches-.xxx inches) from an amount of distance B (i.e., x.xxx inches) ofthe pin member 301. In certain embodiments, the difference in axialseparation (i.e., .xxx inches) may be greater than zero or within arange of between about 0.0005 inches to about 0.015 inches. In otherembodiments, the difference in axial separation may be about 0.003inches.

Referring now to FIG. 4B, a top view of engaging wedge threads on steps31, 32 of connection 300 during makeup in accordance with one or moreembodiments of the present disclosure is shown. Because of the reducedaxial separation between steps 31, 32 of the box member 302,corresponding flanks on the two steps 31, 32 may engage at differenttimes during makeup. In this case, on step 31, corresponding load flanks125, 126 may engage prior to corresponding stab flanks 131, 132, whileon step 32, corresponding stab flanks 133, 134 may engage prior tocorresponding load flanks 127, 128.

FIGS. 4C and 4D show the reduced box step-to-step wedge threadconnection 300 of FIGS. 4A and 4B at a final makeup in accordance withone or more embodiments of the present disclosure. At final makeup, loadflanks 125, 126 and stab flanks 131, 132 on the first step 31 and loadflanks 127, 128 and stab flanks 133, 134 on the second step 32 areengaged. However, an amount of interference between engaged stab andload flanks differs. As such, on first step 31, a higher interference135 (illustrated as overlap) is generated between load flanks 125, 126than stab flanks 131, 132, while on the second step 32, a higherinterference 137 (illustrated as overlap) is generated between stabflanks 133, 134 than load flanks 127, 128 due to the difference in axialseparation between steps 31, 32 of the pin member 301 and box member302. In certain embodiments, on step 31, load flanks 125, 126 may engagewhile stab flanks 131, 132 may not completely engage or engage at all,while on step 32, stab flanks 133, 134 may engage while load flanks 127,128 may not completely engage or engage at all.

In certain embodiments with the reduced box step-to-step connection, amid-seal may be formed in mid-step region 901 as corresponding metalsurfaces of the pin and box members in the mid-step region 901 betweensteps 31, 32 may engage to form a metal-to-metal mid-seal. As shown inFIGS. 4C and 4D, the forces applied to the mid-step region 901 due toincreased interference on outwardly facing flanks (or stated otherwise,flanks facing away from the mid-step region 901), i.e., load flanks 125,126 on step 31 and stab flanks 133, 134 on step 32, further forces metalsurfaces of the mid-seal to remain in contact due to a Poisson effect inthe mid-seal region. In essence, due to the reduced box step-to-stepwedge, tension is created in the box member causing a central portion(mid-step region 901) to “neck” inward (i.e., move radially inward). Atthe same time, due to the reduced box step-to-step wedge, compression iscreated in the pin member causing a central portion (mid-step region)901 to “bow” outward (i.e., move radially outward). Thus, thecorresponding inwardly necked central portion of the box member and theoutwardly bowed central portion of the pin member cause a radialincreased interference (due to the Poisson effect) between metalsurfaces in the mid-step region 901 of the pin and box members.

The axial increased interference created in load flanks 125, 126 on thefirst step 31 and stab flanks 133, 134 on the second step 32 in thereduced box step-to-step wedge thread connection may cause a mid-stepregion 901 of the box member 302 to stretch at final makeup, effectivelypre-tensioning the box member 302. In addition, a mid-step region 901 ofthe pin member 301 may be pre-compressed. By having pre-loaded members,i.e. a pre-tensioned box member 302 and a pre-compressed pin member 301after makeup, the threaded connection 300 may be able to delay thereduction of the mid-seal increased interference that externalcompressive or tensile forces acting on the string may cause on themid-seal. For example external tension forces acting on the connectionmay produce, in the mid-seal sealing surface of the pin member, areduction of the interference contact stresses. However, the precompression of the pin mid step region delays the effect of suchexternal tensile forces, because the pre-compression needs to be firstovercome by the external tensile force before the mid step region isaffected. Similarly, external compression forces acting on theconnection may produce, in the mid-seal sealing surface of the boxmember, a reduction of the interference contact stresses. However, thepre tension of the box mid step region delays the effect of suchexternal compressive forces, because the pre-tension needs to be firstovercome by the external compressive force before the mid step region isaffected.

Wedge threads in combination with dovetail thread profiles may provide aradial interlocking effect, which locks the pin member and box membertogether radially and provides resistance against separation caused byinternal or external pressure. In addition, the step-to-step wedgeintroduces a backup interlocking mechanism. If the standard wedge failsto provide such interlocking, the step-to-step wedge may provideadditional resistance to the internal or external pressure and preventradial separation of the pin and box members. In sum, embodimentsdisclosed herein provide a connection that obtains the trapping effectfor the metal to metal seal in the central portion 901, from thestep-to-step wedge, in combination with the interlocking effect of thedovetail thread profile in the individual steps. Moreover, even if thewedge thread of the individual steps would happen to fail, (due to, forexapmple, standoff caused either by dope entrapment or by insuficientmake up torque), the trapping or interlocking effect may still beprovided by the step-to-step wedge. In certain embodiments, internalpressure support in the connection may be distributed approximatelytwo-thirds to the box thickness at the mid-seal and one-third to thelocking effect of the step-to-step wedge.

Referring now to FIG. 6, a cross-section view of a two-step wedge threadconnection 600 having the step-to-step wedge and also having a mid-sealin accordance with one or more embodiments of the present disclosure isshown. The pin member 601 and box member 602 having corresponding steps31, 32 are engaged such that sealing surfaces 603 (of pin member 601)and 604 (of box member 602) engage. The sealing surfaces 603, 604 areestablished at assembly by metal-to-metal interference. Upon fullmake-up of the connection 600, engagement of the step-to-step wedge mayinduce additional radial positional interference into the contactingsealing surfaces 603, 604 (i.e., an “increased interference” effect). Inaddition to this, the pre-loading of pin and box members due to thestep-to-step wedge may delay the reduction of the Poisson effect (i.e.,the neck inward and bow outward mechanism) that compressive or tensileloads acting on the connection (i.e. forces transmitted by the pipestring) may produce. The seal pressure retention characteristic of thethreaded connection 600 is related to the ability of the sealingsurfaces 603, 604 to remain in contact with one another as radialdeflection of the joint occurs from either internal pressure of externalpressure. Seal retention of embodiments having a locked-in or trappedmid-seal result from a locking effect of the step-to-step wedge therebypreventing loss of surface contact between surfaces 603 and 604. Thelocking in effect causes the two surfaces 603 and 604 to deflect as one.

Methods of making up a reduced box step-to-step connection includeengaging pin wedge threads 306 of pin member 301 with corresponding boxwedge threads 307 of box member 302. During makeup, on step 31,corresponding load flanks 125, 126 may engage prior to correspondingstab flanks 131, 132, while on step 32, corresponding stab flanks 133,134 may engage prior to corresponding load flanks 127, 128. As makeup ofthe connection continues, interference between load flanks 125, 126 onthe first step 31 and stab flanks 133, 134 increases up to a finalmakeup. At final makeup, stab flanks 131, 132 on the first step 31 andload flanks 127, 128 on the second step 32 also engage. Thus, at finalmakeup, a higher interference 135 is generated between load flanks 125,126 than stab flanks 131, 132, while on the second step 32, a higherinterference 137 is generated between stab flanks 133, 134 than loadflanks 127, 128.

Referring now to FIG. 5A, a cross section of a two-step wedge threadconnection 400 having a step-to-step wedge in accordance with one ormore embodiments of the present disclosure is shown. The connection 400includes a pin member 401 having pin wedge threads 406 thereon and a boxmember 402 have box wedge threads 407 thereon. Further, the pin member401 and box member 402 each have corresponding first steps 31 and secondsteps 32 formed thereon. A mid-step region 901 is located betweencorresponding steps 31, 32.

The connection 400 is configured such that a distance B (i.e., axialseparation of the two wedge thread steps 31, 32 of the pin member 401)may be slightly less than distance A (i.e., axial separation of the twowedge thread segments 31, 32 of the box member 402). In this instance,the two-step wedge thread connection may be termed a “reduced pinstep-to-step wedge thread connection” because the axial separation,distance B, between steps 31, 32 of the pin member 401 is reduced. Asshown, distance B of the pin member 401 is reduced by a specified amount(i.e., x.xxx inches-.xxx inches) from a specified amount of distance A(i.e., x.xxx inches) of the box member 402. In certain embodiments, thedifference in axial separation (i.e., .xxx inches) may be within a rangeof between about 0.0005 inches to about 0.015 inches. In otherembodiments, the difference in axial separation may be about 0.003inches.

Referring now to FIG. 5B, a top view of engaging threads on steps 31, 32of connection 400 during makeup in accordance with one or moreembodiments of the present disclosure is shown. Because of the reducedaxial separation between steps 31, 32 of the pin member 401,corresponding flanks on the two steps 31, 32 may engage at differenttimes during makeup. In this case, on step 31, corresponding stab flanks131, 132 may engage prior to corresponding load flanks 125, 126, whileon step 32, corresponding load flanks 127, 128 may engage prior tocorresponding stab flanks 133, 134.

FIGS. 5C and 5D show the reduced pin step-to-step wedge threadconnection 400 at a final makeup in accordance with one or moreembodiments of the present disclosure. At final makeup, load flanks 125,126 and stab flanks 131, 132 on the first step 31 and load flanks 127,128 and stab flanks 133, 134 on the second step 32 are engaged. However,an amount of interference between engaged stab and load flanks differs.On the first step 31, a higher interference 135 (illustrated as overlap)is generated between stab flanks 131, 132 than load flanks 125, 126,while on the second step 32, a higher interference 137 (illustrated asoverlap) is generated between load flanks 127, 128 than stab flanks 133,134, due to the difference in axial separation between steps 31, 32 ofthe pin member 401 and box member 402. In certain embodiments, on step31, stab flanks 131, 132 may engage while load flanks 125, 126 may notcompletely engage or engage at all, while on step 32, load flanks 127,128 may engage while stab flanks 133, 134 may not completely engage orengage at all.

Methods of making up a reduced pin step-to-step connection includeengaging pin wedge threads 406 of pin member 401 with corresponding boxwedge threads 407 of box member 402. During makeup, on step 31,corresponding stab flanks 131, 132 may engage prior to correspondingload flanks 125, 126, while on step 32, corresponding load flanks 127,128 may engage prior to corresponding stab flanks 133, 134. As makeup ofthe connection continues, interference between stab flanks 131, 132 onthe first step 31 and load flanks 127, 128 on second step 32 increasesup to a final makeup. At final makeup, load flanks 125, 126 on the firststep 31 and stab flanks 133, 134 on the second step 32 also engage.Thus, at final makeup, on the first step 31, a higher interference 135is generated between stab flanks 131, 132 than load flanks 125, 126,while on the second step 32, a higher interference 137 is generatedbetween load flanks 127, 128 than stab flanks 133, 134.

In one or more embodiments disclosed herein, the threaded connection maybe a two-step wedge thread connection having a standard wedge on bothsteps, i.e., the thread lead on both steps 31, 32 have wedge ratios thatare substantially the same. In other embodiments, the threadedconnection may have a thread lead on the first step 31 having a firstwedge ratio and a thread lead on the second step 32 having a secondwedge ratio (i.e., different wedge ratios on each step). As previouslydescribed, one of the wedge ratios may be considered to be an“aggressive” wedge ratio and the other a “conservative” wedge ratio(“aggressive” refers to the larger wedge ratio, and “conservative”refers to the smaller wedge ratio). In one or more embodiments disclosedherein, thread leads on one step may have an aggressive wedge ratio ofbetween about 0.035 and 0.045 inches per revolution while the threadleads on the other step may have a conservative wedge ratio of betweenabout 0.003 and 0.010 inches per revolution. In other embodiments, thethread leads on one step may have an aggressive wedge ratio of about0.019 inches per revolution and the thread leads on the other step mayhave a conservative wedge ratio of about 0.011 inches per revolution.

Further, the wedge threads on steps 31, 32 of the threaded connectionmay have a number of different clearance/interference combinationsbetween corresponding roots and crests. For example, in certainembodiments, the threads on one or both steps 31, 32 may have aroot/crest clearance at a final makeup. In other embodiments, thethreads on one or both steps 31, 32 may have root/crest interference ata final makeup. Still further, in certain embodiments, the threads onthe first step 31 may have a root/crest clearance while the threads onthe second step 32 have a root/crest interference, or vice versa. Stillfurther, in certain embodiments, the threads on the first step 31 andsecond step 32 may have alternating root/crest clearance andinterference in adjacent threads.

In certain embodiments, the threaded connection may include a vanishingthread form as shown in FIG. 6. FIG. 6 shows a cross-section view of atwo-step wedge thread connection 700 have a step-to-step wedge. Asshown, the pin member 701 and box member 702 have corresponding steps 31and 32 with pin and box threads 706, 707 thereon, and a mid-step region901 therebetween. Further, the box thread 707 has a thread height thatdiminishes along an axial length of the threads moving away from adistal end of the box member 702. The box thread 707 may becharacterized as a vanishing thread form because of the diminishingthread height.

As used herein, “vanishing” threads may be defined as box threads whichrather than being “perfect” full form threads, vanish when the threadtaper intersects the pipe body surface. Therefore, “vanishing” threadshave their crests truncated, thus leaving a radial gap between thethread crests and the thread root of the mating member. The “vanishing”thread concept may enhance both tension and compression capabilities ofintegral connections when applied to sections of full pipe body wallthickness. It matters not whether the full pipe body wall thicknesssection occurs in a plain end pipe section or in a swaged pipe bodysection as long as the OD of the section is comprised of pipe bodysurface (non-machined) and the ID of the section is comprised of pipebody surface (non-machined).

In a threaded connection, the tension critical section works off of thethread load flank at the thread root. When a “perfect” full form threadintersects the pipe body surface, the critical section is a function ofthe pipe body inner and outer surfaces minus the depth of the “perfect”full form thread. When the thread is allowed to “vanish” into the pipebody surface, a thread with less than full thread height is intersectingthe pipe body surface. A load flank that is less than fully engaged withthe mating member can carry the full tension load applied to theconnection. In certain embodiments, approximately 30%-70% thread loadflank engagement may carry the full tension load. Therefore, theconnection critical section area may be significantly increased bytaking advantage of a “vanishing” thread. For wedge threads, compressioncapacity works off of the thread stab flank at the thread crest. So ifthe thread form intersects the pipe body surface in a section of thefull pipe body wall thickness, whether at a “perfect” thread form heightor just partially as in a “vanishing” thread, the compression capacityof the connection is equal to that of the pipe body.

Embodiments disclosed herein for the step-to-step wedge threadconnection provide a number of advantages. First, embodiments disclosedherein address dope compound entrapment within the wedge threads, whichis an inherent problem in larger diameter wedge products, and subsequentlow break-out torques experienced as the thread compound pressurerelieves with time, loading, or temperature. Even if individual wedgestrap the dope compound, the substantial wedging effect that is createdbetween the two steps of the connection is still sufficient to providerequired break-out torque resistance. Thus, dope entrapment is toleratedby the step-to-step wedge such that it is no longer deleterious to thestructural integrity of the threaded connection.

Next, embodiments disclosed herein address manufacturing limitationsinvolved with thread machining. Generally, a thread is cut on a tubularusing a substantially constant thread lead (including the load lead andthe stab lead), however, some variance in the thread lead occurs duringthe manufacturing process, which is typically includes machining with amill or lathe. During machining, the variance in the thread leadmanifests as a slight periodic variation in the thread lead above andbelow the intended value for the thread lead. This phenomenon iscommonly referred to as “thread drunkenness.” The sensitivity of threaddrunkenness may be determined as a ratio of the magnitude of thevariations or “bumps” in the thread flanks and a width of the wedgethread itself. Previously, the width of the wedge thread was just thedistance between opposing thread flanks themselves (i.e., distancebetween opposing stab and load flanks). Instead, embodiments disclosedherein re-establish a width of the wedge as the distance across thesteps of opposing stab and load flanks, thereby increasing the width ofthe wedge. This effectively reduces the sensitivity of threaddrunkenness and thereby reduces or eliminates manufacturing limitationspreviously caused by thread machining operations.

Still further, embodiments disclosed herein allow the threadedconnection to withstand multiple make-ups and break-outs without losingenergy retention in the wedge thread. Because of the wedging effect thatis created across the two steps, a higher spring effect may be createdover a larger distance. This allows the connection to retain energybetter and allow for increased energy retention in the wedge overmultiple uses. The spring effect also reduces the chances of galling thethread surfaces during make-up of the connection.

While the present disclosure has been described with respect to alimited number of embodiments, those skilled in the art, having benefitof this disclosure, will appreciate that other embodiments may bedevised which do not depart from the scope of the disclosure asdescribed herein. Accordingly, the scope of the disclosure should belimited only by the attached claims.

1. A threaded connection comprising: a pin member comprising a first pinstep and a second pin step, and pin wedge threads disposed on each ofthe first and second pin steps; and a box member comprising a first boxstep and a second box step, and box wedge threads disposed on each ofthe first and second box steps; wherein an axial separation of the firstand second pin steps differs from an axial separation of the first andsecond box steps.
 2. The threaded connection of claim 1, wherein theaxial separation of the first and second box steps is less than theaxial separation of the first and second pin steps.
 3. The threadedconnection of claim 2, further comprising: corresponding stab flanks andload flanks on the corresponding first pin and box steps, wherein thecorresponding load flanks are configured to engage before thecorresponding stab flanks on the corresponding first pin and box steps;and corresponding stab flanks and load flanks on the correspondingsecond pin and box steps, wherein the corresponding stab flanks areconfigured to engage before the corresponding load flanks on thecorresponding second pin and box steps.
 4. The threaded connection ofclaim 1, wherein the axial separation of the first and second pin stepsis less than the axial separation of the first and second box steps. 5.The threaded connection of claim 4, further comprising: correspondingstab flanks and load flanks on the corresponding first pin and boxsteps, wherein the corresponding stab flanks are configured to engagebefore the corresponding load flanks on the corresponding first pin andbox steps; and corresponding stab flanks and load flanks on thecorresponding second pin and box steps, wherein the corresponding loadflanks are configured to engage before the corresponding stab flanks onthe corresponding second pin and box steps.
 6. The threaded connectionof claim 1, further comprising a threadless mid-step region disposedbetween the first and second pin and box steps.
 7. The threadedconnection of claim 6, further comprising a metal-to-metal mid-sealdisposed between the first and second pin and box steps.
 8. The threadedconnection of claim 1, wherein corresponding pin and box wedge threadson the first steps have a first wedge ratio and the corresponding pinand box wedge threads on the second steps have a second wedge ratio. 9.The threaded connection of claim 8, wherein the corresponding pin andbox wedge threads on the first steps engage before the corresponding pinand box wedge threads on the second steps.
 10. The threaded connectionof claim 8, wherein the corresponding pin and box wedge threads on thefirst steps engage after the corresponding pin and box wedge threads onthe second steps.
 11. The threaded connection of claim 8, wherein thecorresponding pin and box wedge threads on the first steps engagesimultaneously with the corresponding pin and box wedge threads on thesecond steps.
 12. The threaded connection of claim 1, wherein an axialseparation of the first and second pins steps differs from an axialseparation of the first and second box steps by between about 0.0005inches and about 0.015 inches.
 13. The threaded connection of claim 1,wherein an axial separation of the first and second pins steps differsfrom an axial separation of the first and second box steps by about0.002 and 0.005 inches.
 14. The threaded connection of claim 1, whereinan axial separation of the first and second pins steps differs from anaxial separation of the first and second box steps by about 0.003inches.
 15. The threaded connection of claim 1, wherein an axialseparation of the first and second pins steps differs from an axialseparation of the first and second box steps by about 0.0005 times theOD of the pipe.
 16. The threaded connection of claim 1, wherein the pinand box wedge threads comprise a generally dovetail-shapedcross-section.
 17. The threaded connection of claim 1, wherein clearanceexists between roots and crests of the pin and box wedge threads on boththe corresponding first and second pin and box steps at a final makeup.18. The threaded connection of claim 1, wherein interference existsbetween roots and crests of the pin and box wedge threads on both thecorresponding first and second pin and box steps at a final makeup. 19.The threaded connection of claim 1, wherein clearance exists betweenroots and crests of the pin and box wedge threads on the correspondingfirst pin and box steps, and interference exists between roots andcrests of the pin and box wedge threads on the corresponding second pinand box steps at a final makeup.
 20. The threaded connection of claim 1,wherein interference exists between roots and crests of the pin and boxwedge threads on the corresponding first pin and box steps, andclearance exists between roots and crests of the pin and box wedgethreads on the corresponding second pin and box steps at a final makeup.21. The threaded connection of claim 1, wherein interference existsbetween roots and crests of the pin and box wedge threads on thecorresponding first pin and box steps, and clearance exists betweenroots and crests of the pin and box wedge threads on the correspondingsecond pin and box steps at a final makeup.
 22. The threaded connectionof claim 1, wherein the pin wedge threads and the box wedge threadsinterfere at thread roots and crests over all or a portion of the pinwedge threads and the box wedge threads.
 23. The threaded connection ofclaim 1, wherein the pin wedge threads and the box wedge threadsinterfere at thread roots on the first corresponding box and pin stepsand at thread crests on the second corresponding box and pin steps,wherein there is a radial clearance between thread roots on the secondcorresponding box and pin steps and thread crests of the firstcorresponding box and pin steps.
 24. The threaded connection of claim 1,further comprising a vanishing box thread on the box member, wherein athread height of the box thread diminishes along an axial length of thebox thread.
 25. A threaded connection comprising: a pin membercomprising a first pin step and a second pin step, and pin wedge threadsdisposed on each of the first and second pin steps; and a box membercomprising a first box step and a second box step, and box wedge threadsdisposed on each of the first and second box steps; wherein the pinwedge threads on at least one of the first and second pin steps and thecorresponding box wedge threads on at least one of the first and secondbox steps are axially misaligned.
 26. A method of making up a threadedconnection, the method comprising: rotationally engaging a pin memberhaving pin wedge threads with a box member having corresponding boxwedge threads, wherein the pin and box wedge threads are formed oncorresponding first and second pin and box steps of the pin and boxmembers; and engaging opposing pin and box stab and load flanks atdifferent times during makeup of the threaded connection.
 27. The methodof claim 26, further comprising: engaging corresponding load flanksbefore stab flanks on the corresponding first pin and box steps;engaging corresponding stab flanks before load flanks on thecorresponding second pin and box steps.
 28. The method of claim 26,further comprising: engaging corresponding stab flanks before loadflanks on the corresponding first pin and box steps; engagingcorresponding load flanks before stab flanks on the corresponding secondpin and box steps.
 29. The method of claim 26, further comprisingengaging corresponding metal sealing surfaces disposed between first andsecond pin and box steps.